1. Field of the Invention
The present invention relates to a liquid crystal display apparatus in which display pixels each comprising a plurality of sub pixels are arranged in a matrix form, a portable device equipped with the liquid crystal display apparatus, and a drive method for the liquid crystal display apparatus.
2. Description of the Related Art
Display apparatuses capable of displaying a stereoscopic image have been studied. As described in Literature “Three-dimensional Display” by Chihiro Masuda, published by Sangyo Tosho Publishing Co., Ltd., for example, Euclid, a Greek mathematician, contemplated in 280 B.C. that a stereoscopy is a feeling obtained as both the right and left eyes simultaneously see different images of a same object as seen from different directions. That is, a stereoscopic image display apparatus should have the function of providing the right and left eyes with images having parallax.
As one specific way of achieving the function, multiple stereoscopic image display systems have been studied, which are classified into a type which uses glasses and a glass-less type. The type that uses glasses includes an anaglyph type which uses color differences, and a polarizing glass type which uses polarization. As a user of the glass using type cannot avoid annoyance of wearing glasses, intensive studies have recently been made on the glass-less type which does not use glasses. The glass-less type includes a lenticular lens type and a parallax barrier type.
The parallax barrier type was conceived by Berthier in 1896 and validated by Ives in 1903. As shown in FIG. 1, a parallax barrier 105 is a barrier (light-shielding plate) having multiple vertically striped thin openings or slits 105a formed. A liquid crystal display panel 106 is arranged close to one top surface of the parallax barrier 105. On the display panel 106, right-eye pixels 123 and left-eye pixels 124 are alternately arranged in a direction orthogonal to the lengthwise direction of the slits 105a. A light source 108 is arranged close to one other top surface of the parallax barrier 105, i.e., on the opposite side to the display panel 106.
Light which has been emitted from the light source 108, has passed the openings (slits 105a) of the parallax barrier 105 and has transmitted the right-eye pixels 123 becomes a light beam 181. Likewise, light which has been emitted from the light source 108, has passed the slits 105a and has transmitted the left-eye pixels 124 becomes a light beam 182. At this time, the position of an observer at which a stereoscopic image is recognizable is determined by the positional relationship between the parallax barrier 105 and the pixels. Specifically, a right eye 141 of an observer 104 should lie in a region where the entire light beam 181 corresponding to a plurality of right-eye pixels 123 passes, and a left eye 142 of the observer 104 should lie in a region where the entire light beam 182 corresponding to a plurality of left-eye pixels 124 passes. This is the case where in FIG. 1, the center, 143, of the right eye 141 and the left eye 142 of the observer is positioned in a rectangular stereoscope visible region 107 shown in FIG. 1.
Of lines that extend in the layout direction of the right-eye pixels 123 and the left-eye pixels 124 in the stereoscope visible region 107, lines which pass through an intersection 107a of diagonal lines in the stereoscope visible region 107 become the longest. With the center 143 positioned at the intersection 107a, the allowance when the position of the observer is shifted in the right-left direction becomes maximum, so that the position of the intersection 107a is the most preferable as the position of observation. In this stereoscopic image display method, therefore, the distance between the intersection 107a and the display panel 106 is taken as an optimal observation distance OD and the observer is recommended to make observation at this distance. An imaginary plane on which the distance from the display panel 106 in the stereoscope visible region 107 becomes the optimal observation distance OD is called an optimal observation plane 107b. Accordingly, lights from the right-eye pixels 123 and the left-eye pixels 124 respectively reach the right eye 141 and the left eye 142 of the observer. This allows the observer to recognize an image displayed on the display panel 106 as a stereoscopic image.
The parallax barrier type, when conceived, had the parallax barrier located between the pixels and the eyes, which brought about an annoyance and a low visibility. The recent achievement of liquid crystal display panels has made it possible to lay out the parallax barrier 105 at the back of the display panel 106 as shown in FIG. 1, thereby resulting in an improved visibility. Accordingly, intensive studies have been made on stereoscopic image display apparatuses of the parallax barrier type at present.
An example of the actual product using the parallax barrier system is described in Literature “Nikkei Electronics No. 838, pp. 26 to 27, issued on Jan. 6, 2003”. The product is a mobile telephone equipped with a 3D-adapted liquid crystal display panel which constitutes a stereoscopic image display apparatus and has a size of 2.2 inches in diagonal with display dots of 176 dots horizontal×220 dots vertical. The liquid crystal display panel has a liquid crystal panel for switches that enable and disable the effect of the parallax barrier, and can change the display mode between stereoscopic display and two-dimensional display. The display definition of the apparatus in two-dimensional image display mode is 128 dpi both in the vertical direction and the horizontal direction. In stereoscopic display mode, however, the apparatus alternately displays an image for the left eye and an image for the right eye in a vertical stripe pattern as mentioned above, so that the horizontal display definition is 64, a half the vertical display definition of 128 dpi.
The lenticular lens type was invented by Ives et al. in about 1910 as described in, for example, the aforementioned Literature “Three-dimensional Display” by Chihiro Masuda, published by Sangyo Tosho Publishing Co., Ltd. FIG. 2 is a perspective view showing a lenticular lens, and FIG. 3 is an optical model diagram showing a stereoscopic image display method which uses a lenticular lens. As shown in FIG. 2, a lenticular lens 121 has one side flat, and the other side on which a plurality of barrel projections (cylindrical lenses 122) extending in one direction are formed in such a way as to be in parallel to one another in the lengthwise direction.
As shown in FIG. 3, in the stereoscopic image display apparatus of the lenticular lens type, the lenticular lens 121, the display panel 106 and the light source 108 are arranged in order from the observer's side, and the pixels of the display panel 106 are positioned at the focal plane of the lenticular lens 121. On the display panel 106, the pixels 123 for displaying an image for the right eye 141 and the pixels 124 for displaying an image for the left eye 142 are alternately arranged. A group of the adjoining pixels 123 and pixels 124 corresponds to each cylindrical lens (projecting portion) 122 of the lenticular lens 121. Accordingly, light rays from the light source 108 which have transmitted through the individual pixels are adequately directed toward the right and left eyes by the cylindrical lenses 122 of the lenticular lens 121. This allows the right and left eyes of an observer to identify different images, so that the observer can recognize a stereoscopic image.
The parallax barrier type “hides” unnecessary light rays with the barrier, whereas the lenticular lens type changes the travel direction of light rays and, in principle, the provision of the lenticular lens does not reduce the brightness of the display screen. In this respect, it seems promising to adapt the lenticular lens type particularly to portable devices or the like for which the high luminance display and low power consumption are important factors.
A developed example of the stereoscopic image display apparatus of the lenticular lens type is described in Literature “Nikkei Electronics No. 838, pp. 26 to 27, issued on Jan. 6, 2003”. The liquid crystal display panel which constitutes the stereoscopic image display apparatus has a size of 7 inches in diagonal with display dots of 800 dots horizontal×480 dots vertical. The display mode can be changed between stereoscopic display and two-dimensional display by changing the distance between the lenticular lens and the liquid crystal display panel by 0.6 mm. The number of horizontal view points is five, so that five different images can be seen as the angle is changed in the horizontal direction. To display five different images, however, the horizontal resolution in stereoscopic image display mode is reduced to ⅕ of the resolution in two-dimensional image display mode.
As disclosed in Japanese Patent Publication No. Hei6-332354, for example, a multi-image simultaneous display has been developed as an image display apparatus using a lenticular lens. This display simultaneously displays images different from one another in different observation directions using the light directing function of the lenticular lens. This can allow the multi-image simultaneous display to provide a plurality of observers, positioned in different directions with respect to the display, with different images simultaneously. Japanese Patent Publication No. Hei6-332354 describes that the use of the multi-image simultaneous display can reduce the layout space and the electric charge or the like as compared with the case where displays equal in number to persons involved.
The following will describe the structure of, and drive method for the liquid crystal display panel to be installed in the above-described stereoscopic image display apparatus. FIG. 4 is a circuit diagram showing the liquid crystal display panel portion of an active matrix type liquid crystal display apparatus. As shown in FIG. 4, the liquid crystal display apparatus is provided with a liquid crystal display panel 1, and a gate line drive circuit 8 and a data line drive circuit 9 which are connected to the liquid crystal display panel 1. The liquid crystal display panel 1 comprises two substrates (not shown) provided in parallel and apart from each other, and a liquid crystal layer (not shown) provided between the two substrates. One substrate is a pixel circuit substrate, and the other one is an opposing substrate.
The pixel circuit substrate is provided with a transparent substrate of glass or the like, a plurality of gate lines 3 provided on the transparent substrate and extending in one direction (hereinafter called “horizontal direction”), and a plurality of data lines 2 provided on the transparent substrate and extending in a direction orthogonal to the extending direction (horizontal direction) of the gate lines 3 (the orthogonal direction will hereinafter be called “vertical direction”). One ends of the gate lines 3 are connected to the gate line drive circuit 8, and one ends of the data lines 2 are connected to the data line drive circuit 9. A TFT (Thin Film Transistor) 4 is provided at the closest point of each data line 2 and each gate line 3. The gate line 3 is connected to the gate of the TFT 4, the data line 2 is connected to one of the source and drain of the TFT 4, and a pixel electrode 15 is connected to the other one of the source and drain of the TFT 4.
The TFT 4 is turned on or off based on the potential of the gate line 3 to selectively connect the pixel electrode 15 to the data line 2 or set the pixel electrode 15 floating. Connected to the pixel electrode 15 is a storage capacitor 6 which holds a signal voltage during one display period. The opposing substrate is provided with a common electrode 7. A liquid crystal cell 5 is formed by the common electrode 7 of the opposing substrate, each pixel electrode of the pixel circuit substrate and that portion of the liquid crystal layer which lies therebetween.
The operation of the thus constructed liquid crystal display apparatus will be discussed below. The gate line drive circuit 8 sequentially applies a high-level signal to the gate lines 3. That is, the gate line drive circuit 8 scans a plurality of gate lines 3. Accordingly, the TFTs 4 connected to those gate lines 3 to which the high-level signal is applied are turned on at a time. In synchronism with the scanning of the gate lines 3, the data line drive circuit 9 applies a data signal to the data lines 2. As a result, the data signal is applied to the pixel electrode 15 connected to that TFT 4 which is turned on, is stored in the storage capacitor 6, and is applied in each liquid crystal cell 5. As a result, the potential of the gate line 3 connected to the TFT 4 becomes low, so that even after the TFT 4 is turned off, the pixel electrode 15 holds a given potential with respect to the common electrode 7 and a given voltage is applied to the liquid crystal cell 5. This aligns the liquid crystal of the liquid crystal cell 5 by a predetermined angle so that the light transmittance takes a predetermined value. As a result, an image can be formed by the entire liquid crystal display panel.
According to the present invention, the drive method for the liquid crystal display apparatus, generally, AC driving to invert the polarity of the voltage to be applied to the liquid crystal cells every predetermined period is carried out in order to elongate the life of the liquid crystal and ensure high reliability thereof. In other words, the inversion drive system of alternately inverting the polarity of the voltage of the data signal to be applied to the liquid crystal cells of the individual pixels from positive to negative or from negative to positive every time the data signal voltage is reapplied. The inversion drive system includes a frame inversion drive method, a gate line inversion drive method and a dot inversion drive method.
The most basic drive method is the frame inversion drive method which inverts the polarity of the voltage to be applied to the liquid crystal cells frame by frame as disclosed in, for example, Japanese Patent Publication No. Hei2-177679. The “frame” is a one vertical scan period needed to supply one screen of data signals to the entire display screen. FIGS. 5A and 5B are diagrams showing the positive/negative polarity distributions of the pixel electrode voltage when the frame inversion drive method is used. FIG. 5A shows the polarity distribution in one frame (called odd frame), and FIG. 5B shows the polarity distribution in a frame (called even frame) following the odd frame shown in FIG. 5A.
The vertical direction shown in FIGS. 5A and 5B matches with the vertical direction shown in FIG. 4 which is the scanning direction of the gate lines, while the horizontal direction shown in FIGS. 5A and 5B matches with the horizontal direction shown in FIG. 4 along which the gate lines extend. The individual cells shown in FIGS. 5A and 5B correspond to the liquid crystal cells 5 shown in FIG. 4. For the cell (liquid crystal cell) marked “+”, the potential of the pixel electrode is positive (hereinafter simply called “positive polarity”) with respect to the potential of the common electrode. For the cell marked “−”, the potential of the pixel electrode is negative (hereinafter simply called “negative polarity”) with respect to the potential of the common electrode. According to the frame inversion drive method, as shown in FIGS. 5A and 5B, when a specific pixel is driven with the positive polarity in one frame, this pixel is driven with the negative polarity in the next frame. This can ensure the elongated life and high reliability of the liquid crystal.
The frame inversion drive method however has the following problem. As shown in FIGS. 5A and 5B, when the polarities of the voltages to be applied to the liquid crystal are the same over the entire display screen in one frame, the amount of transmitting light changes frame by frame, causing flickering. In other words, the voltage to be applied to the liquid crystal is determined by the potential difference between the common electrode voltage and the pixel electrode voltage, and with a voltage having symmetrical positive and negative polarities is applied, the light transmittance in positive polarity mode becomes equal to the light transmittance in negative polarity mode. When the center level of the common electrode potential slightly shifts from the center level of the data signal potential, the positive and negative polarities of the voltage to be applied to the liquid crystal become asymmetrical, thus changing the light transmittance in positive polarity mode. When the frame frequency is 60 Hz, the variation period of the light transmittance of the liquid crystal cell becomes as low as 30 Hz or so, so that an observer recognizes it as flickering. As capacitive coupling is made between the opposing electrode and the data line or the like and the opposing electrode itself has a resistance, it is difficult to make the potential of the opposing electrode uniform over the entire screen. Even when the polarity of the opposing electrode is adjusted to the best state, the light transmittance differs between positive pixels and negative pixels.
As a solution to this problem, Japanese Patent Publication No. Shou61-275823, for example, discloses the gate line inversion drive method which inverts the polarity of the voltage to be applied to the liquid crystal cells every scan line. FIGS. 6A and 6B are diagrams showing the positive/negative polarity distributions of the pixel electrode voltage when the gate line inversion drive method is used. FIG. 6A shows the polarity distribution in an odd frame, and FIG. 6B shows the polarity distribution in an even frame. The vertical direction and the horizontal direction shown in FIGS. 6A and 6B match with the vertical direction and the horizontal shown in FIG. 4 and FIGS. 5A and 5B.
As shown in FIGS. 6A and 6B, the gate line inversion drive method inverts the polarity in each frame gate line by gate line, and further inverts the polarity of each liquid crystal cell frame by frame. Accordingly, rows of positive pixels and rows of negative pixels are alternately arranged in one screen, thereby averaging a change in light transmittance in the vertical direction, which can reduce flickering.
Japanese Patent Publication No. Shou63-68821 discloses the dot inversion drive method which inverts the polarity of the voltage to be applied to the liquid crystal for each of adjoining pixels. FIGS. 7A and 7B are diagrams showing the positive/negative polarity distributions of the pixel electrode voltage when the dot inversion drive method is used. FIG. 7A shows the polarity distribution in an odd frame, and FIG. 7B shows the polarity distribution in an even frame. The vertical direction and the horizontal direction shown in FIGS. 7A and 7B match with the vertical direction and the horizontal shown in FIG. 4, FIGS. 5A and 5B, and FIGS. 6A and 6B.
As shown in FIGS. 7A and 7B, to execute the dot inversion driving, the data signal is supplied to the pixel electrodes in such a way that its polarity differs for each of the pixels adjoining in the gate line direction, and the polarity of the data signal is inverted every horizontal period in such a way that the polarity of the pixel electrode voltage differs for each of the pixels adjoining in the data direction. Accordingly, positive pixels and negative pixels are alternately arranged in one frame both in the vertical direction and the horizontal direction, thereby averaging a change in light transmittance over the entire screen, which cancels flickering.
Of the frame inversion drive method, the gate line inversion drive method, and the dot inversion drive method, the dot inversion drive method can achieve the best image quality. However, the gate line inversion drive method and the dot inversion drive method need to invert the polarity of the data signal every time the gate line drive circuit scans a single gate line, so that the data lines and the pixel electrodes and the common electrode are charged and discharged every inversion. This undesirably increases power consumption. In this respect, Japanese Patent Publication No. 2001-215469, for example, discloses a multiple-gate-lines inversion drive method as a compromise of the frame inversion drive method and the gate line inversion drive method. This method is intended to accomplish both reduction in flickering and suppression of power consumption by inverting the polarity of the pixel electrode voltage for each of a plurality of gate lines.
The conventional technique however has the following problem. When different images are displayed with respect to a plurality of view points in the multiple-view-points image display apparatus as shown in FIGS. 1 and 3, the resolution of each image drops. For example, the resolution becomes lower in stereoscopic image mode as compared with in two-dimensional image display mode. FIG. 8 is a top view showing sub pixels of the 2-view-point parallax barrier type image display apparatus shown in FIG. 1.
As shown in FIG. 8, one display pixel in stereoscopic image mode comprises two display pixels in two-dimensional image display mode. In stereoscopic image mode, the two display pixels become a left-eye pixel for displaying an image for the left eye and a right-eye pixel for displaying an image for the right eye. Each of the left-eye pixel and the right-eye pixel comprises three primary-color sub pixels, and three slit openings correspond to one display pixel. Specifically, a left-eye red sub pixel 411 and a right-eye green sub pixel 422 correspond to the first slit opening. A left-eye blue sub pixel 413 and a right-eye red sub pixel 421 correspond to the next slit opening. A left-eye green sub pixel 412 and a right-eye blue sub pixel 423 correspond to the next slit opening. Given that the layout pitch of the primary-color sub pixels in the lengthwise direction of the slit opening (vertical direction 11) is a and the layout pitch of the primary-color sub pixels in a direction orthogonal to the slit opening (horizontal direction 12) is b, the following equation 1 is satisfied.a:b=3:1  (Equation 1)
Accordingly, the following equation 2 is satisfied for the display pixel pitch a in stereoscopic image mode in the lengthwise direction of the slit opening and the display pixel pitch b in the direction orthogonal to the lengthwise direction of the slit opening. That is, at the time the stereoscopic image display apparatus shown in FIG. 8 displays a stereoscopic image, one display pixel has a size of a in the lengthwise direction of the slit opening and b in the direction orthogonal to the lengthwise direction.a:c=1:2  (Equation 2)
At the time the stereoscopic image display apparatus shown in FIG. 8 displays a two-dimensional image, the parallax barrier 105 is removed, and one display pixel in stereoscopic image mode is used as two display pixels. The method of removing the parallax barrier is the one disclosed in the aforementioned Literature “Nikkei Electronics No. 838, pp. 26 to 27, issued on Jan. 6, 2003” wherein the parallax barrier is constituted by the liquid crystal panel for switches and the light transmittance of each element of the liquid crystal panel is changed. When a lenticular lens is used in place of the parallax barrier, the effect of the lenticular lens can be canceled out by changing the distance between the display panel and the lenticular lens.
Specifically, in two-dimensional image display mode, the three sub pixels, namely, the left-eye red sub pixel 411, the right-eye green sub pixel 422 and the left-eye blue sub pixel 413, are used as a single display pixel, and the three sub pixels, namely, the right-eye red sub pixel 421, the left-eye green sub pixel 412 and the right-eye blue sub pixel 423, are used as a single display pixel. As a result, one display pixel has a size of a in the lengthwise direction of the slit opening and (c/2) in the direction orthogonal to the lengthwise direction. This however is nothing but doubling of the pixel pitch in the direction orthogonal to the lengthwise direction. Therefore, the resolution in the horizontal direction 12 is reduced to a half in stereoscopic image mode as compared with in two-dimensional image display mode, as per the stereoscopic image display apparatus described in the Literature “Three-dimensional Display” by Chihiro Masuda, published by Sangyo Tosho Publishing Co., Ltd.
The reduction in resolution matters particularly when a stereoscopic image containing character information is displayed and when character information is displayed stereoscopically. As the shape of the display pixels becomes a rectangular shape with the aspect ratio of 1:2, the horizontal resolution drops, so that when a character is displayed, the vertical lines which are constituting elements of the character are partly dropped off. Consequently, the visibility of character display significantly drops. This problem becomes noticeable as the number of view points increases.
According to the prior art technologies concerning the stereoscopic image display apparatus, switching between stereoscopic display and two-dimensional display is carried out over the entire screen, and it is not possible to display a mixture of a stereoscopic image and a two-dimensional image at an arbitrary position.
A similar problem, which is not inherent only to the stereoscopic image display apparatus, generally occurs in display apparatuses which display images of plural view points. That is, when different images are displayed for plural view points, the image resolution in the layout direction of the sub pixels for plural view points becomes lower as compared with the case where a single image is displayed, and the visibility considerably drops, particularly, when displaying characters.